The Schneider process of tempering is based upon the utilization of
the absorption of heat caused by the fusing or melting of a solid
substance, and of the fact that so long as a solid is melting or
dissolving in a liquid substance, the liquid cannot get appreciably
hotter, except locally around the heating surface. The body to be
hardened is plunged at the requisite temperature into a bath
containing the solid melting body, or is kept under pressure in the
solid material of low melting point until the required extraction of
heat has taken place, more solid material being added if necessary as
that originally present melts and dissolves.

Nickel steel armor is made in a similar manner to the steel plates,
the material used in casting the ingot being an alloy of nickel and
steel containing between three and four per cent. of nickel.

The Harvey process of making armor consists in taking an all-steel
plate and carbonizing the face. This carbonizing process is very
similar to the cementation process of producing steel, and by it the
face of the plate is made high in carbon and very hard.

The system invented by Sir Joseph Whitworth, of Manchester, England,
consists in what might be called scale armor. A section of a sample of
the armor represents four plates. The outer layer, one inch thick, is
composed of steel of a tensile strength of 80 tons per square inch;
the second layer, one inch thick, of steel whose tensile strength is
40 tons per square inch; the third and fourth layers, each one-half
inch thickness, of mild steel. The outer layer is in small squares of
about ten inches on a side, and is fastened to the second layer by
bolts at the corners and one in the middle of each square. The surface
is flush. (See Fig. 9.) The end sought by the above system is to break